We just started using MJML (https://mjml.io/) at my work and I can't say enough good things about it. You write your emails in their pseudo-HTML markup language and it outputs valid HTML markup that works in basically every email client, including all the variants of Outlook. They offer a nodeJS CLI tool as well as a very nice WYSIWYG tool for MacOS.
Thanks to this I hope to never have to hand-write or outsource another HTML email again.
So 'schlep' is a new word for me!